Drill stack formation

ABSTRACT

A structure. The structure includes a stack of two or more sheets. Successive sheets in each pair of successive sheets of the stack are adhesively coupled to each other by an adhesive layer consisting of a removable adhesive that is removable if heated to an elevated temperature at which the removable adhesive melts. The removable adhesive is also disposed on top and bottom surfaces of the stack. The removable adhesive consists of a liquid while adhesively coupling the successive sheets to each other. A first surface of a first layer coupled with the removable adhesive to a first surface of the stack. A first surface of a second layer is coupled with the removable adhesive to a second surface of the stack. The first and second layers are adapted to prevent burr formation in a hole subsequently drilled through the stack.

This application is a continuation application claiming priority to Ser.No. 10/691,882, filed Oct. 23, 2003; which is a divisional of U.S. Pat.No. 6,669,805, issued Dec. 30, 2003.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method of temporarily adhering astack of sheets together to facilitate drilling a hole through the stackof sheets.

2. Related Art

A stack of sheets may be adhered together around a periphery of eachsheet using an adhesive such as a glass cloth impregnated with epoxy.Hole burring occurs as a drill passes through the stack. Additionally,each sheet separates from an adjacent sheet as the drill passes betweenthe sheets. This results in the whole stack of sheets expanding. Analternate method includes the permanent application of cured epoxy overthe entire surface of each sheet in the stack. The thickness of theepoxy between each sheet results in excessive thickness of the overallstack as well as composites which will contain the separated sheets whenthey are processed into composites. A method of drilling a stack ofsheets that overcomes these problems plus others is desired.

SUMMARY OF THE INVENTION

A first general aspect of the present invention provides a structurecomprising:

a stack comprising a plurality of sheets such that each successive sheetis coupled with a removable adhesive between each sheet; and

an opening extending through the plurality of sheets within the stack.

A second general aspect of the present invention provides a structurecomprising:

a plurality of stacks wherein each successive stack is coupled with aremovable adhesive to an intermediate layer between each stack whereineach intermediate layer prevents burr formation; and

wherein each stack comprises a plurality of sheets such that eachsuccessive sheet is coupled with a removable adhesive between eachsheet.

A third general aspect of the present invention provides a methodcomprising:

forming a stack by stacking a plurality of sheets;

applying an adhesive between each successive sheet;

applying a vacuum to the plurality of sheets;

heating the plurality of sheets to melt the solid adhesive;

applying a first pressure to the sheets;

cooling the plurality of sheets; and

forming an opening through the plurality of sheets; and

separating the sheets.

A forth general aspect of the present invention provides a methodcomprising:

forming a stack by stacking a plurality of sheets;

applying a thin layer of water between each successive sheet;

applying a pressure to the sheets; and

forming an opening through the plurality of sheets.

BRIEF DESCRIPTION OF THE DRAWINGS

For an understanding of the present invention, reference should be madeto the following detailed description taken in connection with theaccompanying drawings wherein:

FIG. 1 illustrates a first embodiment of the present invention includinga side view of a laminated structure including a stack comprising aplurality of sheets including a removable adhesive between each sheet;

FIG. 2 illustrates a second embodiment of the present inventionincluding a side view of a laminated structure including a plurality ofstacks including a plurality of layers separating each stack;

FIG. 3 illustrates a third embodiment of the present invention includingan exploded side view of another embodiment of a laminated structureincluding a plurality of blotter sheets and a plurality plates added toa stack;

FIG. 4 illustrates the laminated structure of FIG. 3 positioned within apress apparatus for forming a rigid stack;

FIG. 5 illustrates the rigid stack of FIG. 4 with a burr free holedrilled through each sheet of the stack;

FIG. 6 illustrates a plan view of a hole within a sheet of the stack;and

FIG. 7 illustrates a flow chart of a method for producing a burr freehole in each sheet of the stack.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a schematic view of a laminated structure 10including a stack 12 in accordance with a first embodiment. The stack 12includes a plurality of sheets 14A-14L. A removable adhesive 16A-16K isapplied between each sheet 14A-14L, respectively. The sheets 14A-14L maycomprise any suitable material (e.g., copper, invar,copper-invar-copper, etc.). Invar is an iron-nickel alloy. The removableadhesive 16A-16K may comprise any suitable material (e.g., fructose,sucrose, water soluble polymers, water, etc.). The material may compriseany suitable form (e.g., powered fructose, a liquid, a liquid solution,etc.).

FIG. 2 illustrates a laminated structure 10A including a stack 12A inaccordance with a second embodiment. The stack 12A includes a pluralityof stacks 12C, 12D, 12E, and 12F interspersed with a plurality of layers18A-18E. Each stack 12C, 12D, 12E and 12F includes a plurality of sheets14 with removable adhesive placed between each sheet 14. Also, theremovable adhesive 16 is placed between each layer 18A-18E and eachadjacent sheet 14. Each layer 18B and 18C prevents chip build up withindrill bit flutes 21 by providing an interruption in the sheet 14 beingdrilled. Each layer 18A-18E comprises any suitable soft material (e.g.,impregnated and laminated epoxy/glass, phenolic/paper laminate,aluminum, etc.). The formation chips are broken off each time the drillbit 20 passes from one material to a dissimilar material. For example,if each sheet 14 is copper, and each layer 18A-18E is (aluminum orpaper/phenolic), then any tendency for chip build up would beinterrupted each time the drill bit 20 passes from copper to (aluminumor paper/phenolic), or from (aluminum or paper/phenolic) to copper.Additionally, the first layer 18A keeps the drill bit from wandering asit enters the stack 12A of the laminated structure 10A. A soft material,such as aluminum, assists the drill bit 20 in starting a hole 102 at adesired location without wandering about a top surface 22 of the layer18A.

FIG. 3 illustrates a laminated structure 10B including a stack 12B inaccordance with a third embodiment. The stack 12B includes a pluralityof sheets 14. The removable adhesive 16 is applied between each sheet14. The stack 12B includes a first surface 24 and a second surface 26. Afirst surface 28A of a first layer 18F is coupled with the removableadhesive 16 to the first surface 24 of the stack 12B. A first surface30A of a second layer 18G is coupled with the removable adhesive 16 tothe second surface 26 of the stack 12B. A first surface 32A of a firstfoil 34A contacts a second surface 28B of the first layer 18F. A firstsurface 36A of a second foil 34B contacts a second surface 30B of thesecond layer 18G.

A first surface 38A of a first plate 50A contacts a second surface 32Bof the first foil 34A. A first surface 40A of a second plate 50Bcontacts a second surface 36B of the second foil 34B. A first surface42A of a third plate 50C contacts a second surface 38B of the firstplate 50A. A first surface 44A of a fourth plate 50D contacts a secondsurface 40B of the second plate SOB. The plates 50A-50D may include anysuitable material, such as stainless steel.

The laminated structure 10B includes a first blotter pad 60A and asecond blotter pad 60B. The first blotter pad 60A includes at least oneblotter sheet 62, and the second blotter pad 60B includes at least oneblotter sheet 62. The blotter sheets 62 may include any suitablecompressible material, such as paper. The blotter pads 60A and 60Babsorb any misalignment between a pair of pressure surfaces 90A and 90B(FIG. 4) and the stack 12B, so that a uniform pressure is applied to thestack 12B.

A first surface 64A of the first blotter pad 60A contacts a secondsurface 42B of the third plate 50C. A first surface 66A of the secondblotter pad 60B contacts a second surface 44B of the fourth plate 50D. Asecond surface 64B of the first blotter pad 60A contacts a first surface66A of a fifth plate 50E. A second surface 66B of the second blotter pad60B contacts a first surface 68A of a sixth plate 50F. The plates 50Eand 50F may include any suitable material, such as stainless steel.

FIG. 4 illustrates the laminated structure 10B of FIG. 3 positionedwithin a press apparatus 92. The press apparatus 92 includes a firstpressure head 94A, a second pressure head 94B, a vacuum source 96, and aheat source 98. The first pressure head 94A and the second pressure head94B provide a compressive force 100 to the laminated structure 10B. Asecond surface 66B of the fifth plate 50E contacts the pressure surface90A of the first pressure head 94A. A second surface 68B of the sixthplate 50F contacts the pressure surface 90B of the second pressure head94B.

FIG. 7 illustrates a flow chart of a method for producing a burr freehole 102 in each sheet 14 of the stack 12B (FIGS. 5 and 6). Step 104includes stacking a plurality of sheets 14 to form the stack 12B. Step106 includes applying a removable adhesive 16 between each successivesheet 14 in the stack 12B. Step 108 includes applying the removableadhesive 16 between the first layer 18F and the first surface 24 of thestack 12B. As mentioned above, the removable adhesive 16 may compriseany suitable material (e.g., fructose, sucrose, water soluble polymers,water, water solutions, etc.). The following example describes using theremovable adhesive 16 in the form of solid powered fructose. Step 110includes applying the removable adhesive 16 between the second layer 18Gand the second surface 26 of the stack 12B. Step 111 includes formingthe laminated structure 10B by applying the foil sheets 34A, 34B the50A-50F, and the blotter pads 60A and 60B to the stack 12B, asillustrated in FIG. 7. Step 112 includes applying a vacuum to thelaminated structure 10B using the vacuum source 96. Step 114 includesheating the laminated structure 10B to melt the removable adhesive 16.

Step 116 includes applying the compressive force 100 to the laminatedstructure 10B. For fructose, the heat source 98 provides a temperatureof about 50° C. to 200° C. and a first compressive force 100 applied tothe laminated structure 10B creates a pressure of about 25 to 75 psig.After about 10 to 20 minutes, the fructose particles start to soften,and the pressure is increased to about 200 to 400 psig. The increase inpressure is delayed to ensure that every fructose particle has beensoftened to prevent denting of the sheets 14. The pressure andtemperature are held for about 5 to 15 minutes and then shut off and thelaminated structure 10B is cooled while maintaining pressure. When thestack is cool, the pressure is removed and the laminated structure 10Bis removed from the press apparatus 92.

In step 118, the laminated structure 10B is cooled to an ambienttemperature. In step 119, the foil sheets 34A, 34B, the blotter pads60A, 60B, and the plates 50A-50F are removed from the laminatedstructure, and the stack 12B and the attached layers 18F and 18G areremoved from the press apparatus 92. In step 120, a drill bit 20 drillsthe hole 102 through the stack 12B and the layers 18F and 18G, asillustrated in FIG. 5. In step 122, the stack 12B and the layers 18F and18G are dipped into a liquid solution 132 to dissolve the fructose. Forfructose, the liquid solution 132 may include an ethylene glycol/watermixture. In step 124 the removable adhesive is heated in the liquidsolution 132 temperature of about 130° C. to about 150° C. for about 5minutes to melt the removable adhesive 16. In step 126, the sheets 14are separated from each other using any suitable device, such astweezers, clamping devices, etc. In step 128, each sheet 14 is rinsedwith any suitable liquid, such as, distilled water and/or a milddetergent solution. In step 130 each sheet 14 is dried using a gas, suchas hot dry air. Alternatively, the sheets 14 may be separated by placingthe stack 12B in a steam autoclave 134. In the steam autoclave 134,pressurized steam is driven between each sheet 14. The sheets 14 arethen separated, rinsed in water and dried. FIG. 6 illustrates a planview of the sheet 14 having formed a burr free hole 102.

While embodiments of the present invention have been described hereinfor purposes of illustration, many modifications and changes will becomeapparent to those skilled in the art. For example, the removableadhesive 16A-16K may comprise a thin layer of water. The surface tensionof the thin layer of water between each sheet 14A-14L of the laminatedstructure 10A holds the laminated structure 10A together while the hole102 is drilled. Each sheet 14A-14L is peeled off the laminated structure10A and rinsed in additional water to remove any material particles.Then, each sheet 14A-14L is dried. Accordingly, the appended claims areintended to encompass all such modifications and changes as fall withinthe true spirit and scope of this invention.

1. A structure, comprising: a stack of two or more sheets, whereinsuccessive sheets in each pair of successive sheets of the stack areadhesively coupled to each other by an adhesive layer consisting of aremovable adhesive, wherein the adhesive layer is in direct mechanicalcontact with the successive sheets in each pair, wherein the removableadhesive is also disposed on top and bottom surfaces of the stack, andwherein the removable adhesive consists of a liquid while adhesivelycoupling the successive sheets to each other, and wherein the removableadhesive has a characteristic of being removable if heated to anelevated temperature at which the removable adhesive melts; a firstsurface of a first layer coupled with the removable adhesive to a firstsurface of the stack; and a first surface of a second layer coupled withthe removable adhesive to a second surface of the stack, wherein thefirst and second layers are adapted to prevent burr formation in a holesubsequently drilled through the stack.
 2. The structure of claim 1,wherein the sheets each consist of a material selected from the groupconsisting of copper, invar, copper-invar-copper, aluminum, andmolybdenum.
 3. The structure of claim 1, wherein the removable adhesive,while adhesively coupling the successive sheets to each other, consistsof a water solution.
 4. The structure of claim 1, wherein a continuousopening extends through the stack, the first layer, and the secondlayer.
 5. The structure of claim 1, further including: a first surfaceof a first foil layer contacting a second surface of the first layer,wherein the first foil layer consists of a first foil; and a firstsurface of a second foil layer contacting a second surface of the secondlayer, wherein the second foil layer consists of a second foil.
 6. Thestructure of claim 5, further including: a first surface of a firstplate contacting a second surface of the first foil, wherein the firstplate comprises stainless steel; and a first surface of a second platecontacting a second surface of the second foil.
 7. The structure ofclaim 6, wherein the first and second foil comprises copper.
 8. Thestructure of claim 6, further including: a first surface of a thirdplate contacting a second surface of the first plate; and a firstsurface of the fourth plate contacting a second surface of the secondplate.
 9. The structure of claim 8, further including: a first blotterpad comprising at least one blotter sheet; a first surface of the firstblotter pad contacting a second surface of the third plate; a secondblotter pad comprising at least one blotter sheet; and a first surfaceof the second blotter pad contacting a second surface of the fourthplate.
 10. The structure of claim 9, wherein the first and secondblotter sheet comprises paper.
 11. The structure of claim 9, furtherincluding: a first surface of a fifth plate contacting a second surfaceof the first blotter pad; and a first surface of a sixth platecontacting a second surface of the second blotter pad.
 12. The structureof claim 11, further including: a first pressure head contacting asecond surface of the fifth plate; and a second pressure head contactinga second surface of the sixth plate.
 13. The structure of claim 12,wherein a compressive force is acting upon the stack, the first layer,the second layer, the first foil, the second foil, the first plate, thesecond plate, the third plate, the fourth plate, the first blodder pad,the second blodder pad, the fifth plate, and the sixth plate, andwherein the compressive force is being provided by the first and secondpressure heads.
 14. The structure of claim 13, wherein the stack, thefirst layer, the second layer, the first foil, the second foil, thefirst plate, the second plate, the third plate, the fourth plate, thefirst blodder pad, the second blodder pad, the fifth plate, and thesixth plate are at an elevated temperature in a range of 50° F. to 200°F.
 15. The structure of claim 5, wherein the first and second layercomprises a material selected from the group consisting of impregnatedand laminated epoxy/glass, phenolic/paper laminate, and aluminum. 16.The structure of claim 1, wherein the removable adhesive, whileadhesively coupling the successive sheets to each other, consists of amaterial selected from the group consisting of fructose and sucrose. 17.The structure of claim 1, wherein the removable adhesive, whileadhesively coupling the successive sheets to each other, consists ofwater.
 18. A structure, comprising: a plurality of stacks, wherein eachstack and its adjacent stack of the plurality of stacks are both coupledwith a removable adhesive to an intermediate layer therebetween, whereineach intermediate layer is adapted to prevent burr formation in a holesubsequently drilled through the stack, wherein each stack comprises aplurality of sheets such that each sheet and its adjacent sheet of theplurality of sheets are adhesively coupled to each other with anadhesive layer consisting of the removable adhesive, wherein theadhesive layer is in direct mechanical contact with said each sheet andits adjacent sheet, wherein the removable adhesive consists of a liquidwhile adhesively coupling said each sheet with its adjacent sheet, andwherein the removable adhesive has a characteristic of being removableif heated to an elevated temperature at which the removable adhesivemelts.
 19. The structure of claim 19, wherein the removable adhesive,while adhesively coupling said each sheet with its adjacent sheet,consists of a material selected from the group consisting of water and awater solution.
 20. The structure of claim 19, wherein the removableadhesive, while adhesively coupling said each sheet with its adjacentsheet, consists of water.